Abdomino-thoracic transmission during ACS: facts and figures.

Elevated intra-abdominal pressure (IAP) exerts effects not only on intra-abdominal organs, but also on organs distant to the abdominal compartment. Abdomino-thoracic interaction during intra-abdominal hypertension (IAH) or abdominal compartment syndrome (ACS) interferes with pulmonary, cardiovascular and cerebral function. In accordance with recent guidelines, IAH is defined as IAP above 12 mmHg and ACS as IAP more than 20 mmHg with one or more new organ failures. In this review we will first discuss the effects of elevated IAP on pulmonary dynamics and the relevance for interpreting airway pressures and adjusting ventilator settings. We will then discuss the interaction between abdomino-thoracic pressure transmission and global haemodynamics, the knowledge of which is necessary for correct assessment of cardiac preload and to optimize fluid therapy in the setting of IAH/ACS. A discussion on the relationship between increased IAP, increased intracranial pressure (ICP) and decreased cerebral perfusion pressure (CPP) will follow. Finally, we will review ventilator-induced thoracic pressure swings and their transmission to the abdominal compartment.